1. Field
The present disclosure relates generally to aircraft and, in particular, to providing navigation information to aircraft. Still more particularly, the present disclosure relates to a method and apparatus for sending navigation information to an aircraft to guide the aircraft to a landing site.
2. Background
When an aircraft approaches an airport, navigation information may be received from one or more systems to aid in guiding the aircraft. For example, an instrument landing system (ILS), a microwave landing system (MLS), a global positioning satellite (GPS) system, and other types of systems may be used to provide navigation information to the aircraft for use in guiding the aircraft to a runway.
Augmentation systems on the ground at airports provide information that may be used by the aircraft to increase the accuracy of the global navigation satellite system (GNSS) receiver in the aircraft. The satellites transmit signals processed by these augmentation systems.
These types of augmentation systems transmit correction information for measured satellite pseudo-ranges. The corrections are difference-calculated ranges indicated by the satellites and the known fixed positions. These systems are in a reference position that has been very accurately surveyed.
The receiver in the reference position receives a global navigation satellite system (GNSS) signal and uses the expected ranges derived from the known position to calculate ranging corrections. The augmentation system receives pseudo-ranges from receivers and compares that with expected pseudo-ranges with the difference being an error correction. The process of generating the information is often referred to as augmentation and the error or corrections are also referred to as pseudo-range correction data.
The augmentation system then transmits this pseudo-range correction data to the global navigation satellite system receiver in the aircraft for use in correcting measurements made by the system in the aircraft. This pseudo-range correction data is used by the aircraft to obtain a more accurate location of the aircraft.
Many of these augmentation systems at airports are permanent ground installations with the antennas for receiving signals from the satellites in pre-surveyed locations. In some cases, portability is desired to allow for temporary use at an airport or other location with a runway or landing strip where aircraft may land.
Some augmentation systems that provide pseudo-range correction data are portable and can be moved from one location to another. These currently used portable augmentation systems, however, take an amount of time to set up and become operational that is often longer than desired. The size and complexity of the equipment in the currently used portable augmentation systems causes the time and effort needed to set up the system to be longer than desired. With the complexity of these systems, often times specialized training is needed by human operators to operate and set up currently used portable augmentation systems.
Also, the locations for antennas are identified and set up from surveys of the location made ahead of time. This process is the same as one performed for permanent installations of these systems and also adds to the time needed to set up an augmentation system. As a result, time is needed to perform and obtain a survey for placement of the antennas in the receivers. As a result, setting up currently used portable augmentation systems does not occur as quickly as desired in many cases. For example, a situation may occur in which an aircraft may be diverted to another location for landing in which an augmentation system is not available. In this situation, pseudo-range correction data for the aircraft may not be available as soon as desired depending on the amount of time available to set up a currently used portable augmentation system before information is needed by the aircraft.
As a result, the portability and ease at setting up and using currently used portable augmentation systems are not as great as desired. Therefore, it would be desirable to have a method and apparatus that takes into account at least some of the issues discussed above, as well as other possible issues.